The invention relates to a method and apparatus for controlling the cutting feed of band saw machines for obtaining an optimum feed rate or velocity with the same safety against straying (pulling out of line) of the saw cut.
In band saw machines, for example metal band saws, it is necessary to adapt the cutting feed velocity or the feed force to the stress or load on the saw band produced by the cutting forces. Various methods are known for this purpose. For example, in band saw machines a constant force is exerted on the saw band in the direction of the cutting feed during the cutting operation. Also, a so-called hydraulic cutting force control is known which likewise serves for maintaining a preselectable feed force at a constant value.
These methods and devices are completely satisfactory only in those exceptional cases in which the cutting forces and the distribution thereof remain unchanged during cutting over the entire cutting surface.
Another technical solution of the feed system in band saws resides in a forcible advance of the saw carriage with a constant feed velocity, for example under the control of a hydraulic quantity regulator (governor).
The methods do not take into consideration changes in the cutting force distribution and/or the wear conditions of the saw band. With progressive wearing of the tool, there exists with the latter method the danger of the band straying out of the cut.
All of the aforementioned known methods for the feed control of band saw machines entail the following grave disadvantages:
Even if numerical data material is available for the preselection of the feed force or the feed velocity, great risks are involved in the use thereof by, in most cases, unskilled assistant personnel. If large safety margins are utilized in operation, the machines and tools are then utilized to only a small part of their inherent capacity.
The preselection of a constant feed force or feed velocity represents a considerable compromise in all those instances, in which the cutting force distribution varies over the cross section of the cut material, for example during the sawing of round material. Large losses in performance result, since the adjusted feed value must be chosen according to the most unfavorable conditions.
The low stability of the saw band renders the cutting performance greatly dependent on the wear condition of the tool. In case of constant cutting feed, the adjusted feed value must be selected under consideration of the worn tool.
The invention is based on the following task:
A method and apparatus are to be provided which permit, while excluding the danger of straying, an optimum feed velocity with band saws.
Furthermore, the following partial tasks are also to be solved by the present invention:
The economically optimal cutting feed is to adust itself automatically, i.e. without preselection and independently of the strength or rigidity of the material to be cut.
The shape of the cross section of the material to be sawed is to be constantly taken into account, after preselection at the operating panel, by an appropriate automatic adaptation of the feed rate. Consequently, optimum cutting conditions and thus a maximum cutting performance are to result over the entire cross section.
The blunting or wearing of the saw band is to be considered as well to the full extent during the automatic optimization of the feed velocity. Once the saw band wear reaches a preselectable magnitude, the machine is to be automatically stopped. Additionally, prior to stopping the machine, the wear condition of the tool is to be constantly indicated in a digital fashion.
The method according to this invention is characterized in that the saw band is continuosuly maintained within the critical area of its teeth under a tensile stress adjusted at least approximately to a constant value.
The apparatus for carrying out the method is characterized by means for controlling the tensile stress of the saw band.
These and further objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.